The government should fully investigate how this major breach of national security occurred. But prosecuting Assange would be a mistake.

The first problem with going after Assange is that the effort is likely to fail. Extraditing Assange from England (where he is now) or Sweden (where he may go to face charges of sexual assault) would not be easy, especially since Assange's actions might be deemed a "political offense," for which exceptions are made to extradition obligations.

Even if the U.S. government surmounts this hurdle, a criminal conviction is not assured. The most relevant law, the Espionage Act, is famously overbroad and thus an uncertain basis for prosecution. This is one reason the government has never successfully prosecuted a member of the media for soliciting or publishing classified information. Nor has the government ever successfully prosecuted a non-media organization for solicitation or receipt of classified information.

A failed attempt to prosecute Assange would be worse than not prosecuting him. It would make the United States look even more ineffectual than it does as a result of the leaks.

A successful prosecution, on the other hand, would not achieve the desired deterrent effect. WikiLeaks copycats are quickly proliferating around the globe, beyond the U.S. government's effective reach. A conviction would make a martyr of Assange, embolden copycat efforts and illustrate the limits of American law to stop them.

A conviction would also cause collateral damage to American media freedoms. It is difficult to distinguish Assange or WikiLeaks from The Washington Post. National security reporters for The Post solicit and receive classified information regularly. And The Post regularly publishes it. The Obama administration has suggested it can prosecute Assange without impinging on press freedoms by charging him not with publishing classified information but with conspiring with Bradley Manning, the alleged government leaker, to steal and share the information. News reports suggest that this theory is falling apart because the government cannot find evidence that Assange induced Bradley to leak. Even if it could, such evidence would not distinguish the many American journalists who actively aid leakers of classified information.

One reason journalists have never been prosecuted for soliciting and publishing classified information is that the First Amendment, to an uncertain degree never settled by courts, protects these activities. Convicting Assange would require courts to resolve this uncertainty in a way that narrows First Amendment protections. It would imply that the First Amendment does not prevent prosecution of American journalists who seek and publish classified information. At the very least it would render the First Amendment a less certain shield. This would - in contrast to WikiLeaks copycats outside our borders - chill the American press in its national security reporting.

Many would cheer this result because media publication of classified information has caused significant harm to national security. The press has indeed published many very damaging leaks, especially in the past decade. But stopping journalists from seeking and publishing classified information would cause a different type of damage. Publication of classified information sometimes reveals illegal or imprudent government behavior. More important, fear of leaks causes national security officials to think twice about what they are doing in secret with little direct oversight. Diminishing this fear will diminish a vital form of accountability where it is needed most.

Prosecuting Assange would also raise uncomfortable issues for the government. It is well known that government officials, including senior ones, sometimes disclose classified information to journalists. Attorneys for a State Department contractor who is being prosecuted for leaking classified information have been calling attention to this double standard. Prosecuting Assange would shine a much brighter light on this embarrassing practice. It would also highlight the tension, if not hypocrisy, in the State Department's Internet freedom initiatives as well as its support for broad press freedoms in the current Middle East upheavals.

The government's most prudent course is to ignore Assange and focus instead on tightening the lax security safeguards that allowed the leaks to happen. In the current political environment this is easier said than done, and it will take courage on the part of the attorney general.

Jack Goldsmith teaches at Harvard Law School and served as an assistant attorney general in the Bush administration. He is a member of the Hoover Institution's Task Force on National Security and Law and blogs at www.lawfareblog.com.